More realistic symmetric key export example

A common key exchange operation is that a "client" provides a public (RSA or EC) key to the HSM, the HSM generates a symmetric key encrypted under that public key, and the client then imports the symmetric key into its own keystore. (This is a toy example of how key exchange between HSMs and mobile devices works.) The existing code samples provide hints at how to accomplish each of these steps _except_ importing the public key; [RSAImportKey](https://github.com/aws-samples/aws-cloudhsm-jce-examples/blob/master/src/main/java/com/amazonaws/cloudhsm/examples/RSAImportKey.java) does something similar but in the opposite direction.

An end-to-end example for exporting an AES key using this flow would be welcome.

Start by reviewing the existing code samples and RSAImportKey.java, which demonstrates the related reverse-direction public-key import. Trace how the examples handle public-key import, HSM-generated symmetric keys, and client-side keystore import. Done means an end-to-end example exporting an AES key encrypted under a client RSA or EC public key.

Written by the indexing model from the issue text.